Process for pyrolyzing a solid or liquid hydrocarbonaceous fuel in a fluidized bed

ABSTRACT

A SOLID OR LIQUID HYDROCARBONACEOUS FUEL, SUCH AS BITUMINOUS COAL OR RESIDUAL OIL, IS CHARGED TO A LOWER ZONE OF A FLUIDIZED BED, THIS ZONE COMPRISING COKE PELLETS, WHEREIN THE FUEL IS CARBONIZED OR CRACKED (I.E. PYROLYZED) TO FORM GASEOUS PRODUCTS AND A FRESH COKE ACCRETING UPON THE PELLETS. THE GASEOUS PRODUCTS FLUIDIZE A SUPERPOSED, CONTIGUOUS, UPPER ZONE OF THE FLUIDIZED BED, COMPRISING A SOLID OF SMALLER SIZE AND BEING FLUIDIZED AT LOWER VELOCITY. THE VELOCITY OF THE LOWER ZONE IS SUFFICIENT TO PREVENT THE SMALLER SOLID FROM PENETRATING DEEPLY INTO THE ZONE. HEAT IS SUPPLIED TO THE LOWER ZONE BY HEAT CONDUCTION FROM THE UPPER ZONE. THE HEAT IS EITHER GENERATED WITHIN THE UPPER ZONE (E.G., BY COMBUSTION OR OTHER CHEMICAL REACTION OR BY SUPPLY OF A HOT SOLID TO THE UPPER ZONE AND WITHDRAWAL OF SOLID THEREFROM) OR SUPPLIED THERETO BY INDIRECT HEAT EXCHANGE FROM A HEATING MEDIUM. ALTERNATIVELY, IF THE FUEL CARBONIZATION OR CRACKING IS CONDUCTED IN AN ATMOSPHERE OR HYDROGEN AT A SURRICIENTLY HIGH PARTIAL PRESSURE, SO THAT THE REACTION OF THE FUEL IS EXOTHERMIC, HEAT IS WITHDRAWN FROM THE LOWER ZONE BY HEAT CONDUCTION TO THE UPPER ZONE AND THE HEAT IS REMOVED FROM THE UPPER ZONE, E.G., BY INDIRECT HEAT EXCHANGE TO A COOLING MEDIUM.

g- 3, 1971 A. M. SQUIRES 3,597,327

PROCESS FOR PYROLYZING A SOLID OR LIQUID HYDROCARBONACEOUS FUEL IN AFLUIDIZED BED Filed April 2, .1969 2 Sheets-Sheet 1 FVEA 6'45 M 4 f/E/l77/)6 flan/v4 INVENTOR 6 52% 9 17/7790? #1. SdN/l/PES rams FELL 75 Aug.3, 1971 SQUIRES 3,597,321

PROCESS FOR PYROLYZING A SOLID on LIQUID HYDROCARBONACEOUS FUEL IN AFLUIDIZED BED Filed April z, .1969 2 Sheets-Sheet a my 225 /4/ it"United States Paten 3:1:

3,597 327 PROCESS FOR PYROLYZING A SOLID OR LllQUlD HYDROCARBONACEOUSFUEL IN A F LlUllDIZlED BED Arthur M. Squires, 245 W. 104th t., NewYork, NY. 10025 Continuation-impart of application Ser. No. 561,551,June 29, 1966. This application Apr. 2, 1969, Ser.

lint. or. con; 49/22 US. Cl. 2tl112 12 Claims ABSTRACT OF THE DISCLOSUREA solid or liquid hydrocarbonaceous fuel, such as bituminous coal orresidual oil, is charged to a lower zone of a fluidized bed, this zonecomprising coke pellets, wherein the fuel is carbonized or cracked(i.e., pyrolyzed) to form gaseous products and a fresh coke accretingupon the pellets. The gaseous products fluidize a superposed,contiguous, upper zone of the fluidized bed, comprising a solid ofsmaller size and being fluidized at lower velocity. The velocity of thelower zone is suflicient to prevent the smaller solid from penetratingdeeply into the zone. Heat is supplied to the lower zone by heatconduction from the upper zone. The heat is either generated within theupper zone (e.g., by combustion or other chemical reaction or by supplyof a hot solid to the upper zone and withdrawal of solid therefrom) orsupplied thereto by indirect heat exchange from a heating medium.Alternatively, if the fuel carbonization or cracking is conducted in anatmosphere of hydrogen at a sufficiently high partial pressure, so thatthe reaction of the fuel is exothermic, heat is withdrawn from the lowerzone by heat conduction to the upper zone, and the heat is removed fromthe upper zone, e.g., by indirect heat exchange to a cooling medium.

BACKGROUND OF THE INVENTION This application is a continuation-impart ofmy copending applications Ser. No. 561,551, filed June 29, 1966, and toissue as US. Pat. 3,437,561 on Apr, 8, 1969, and Ser. No. 754,226, filedAug. 21, 1968, now US. Pat. No. 3,481,834.

My aforementioned application Ser. No. 561,551, to become US. Pat.3,437,561, disclosed a technique for hydrocarbonizing coal in anagglomerating fluidized bed, to form pellets of coke and a gas rich inmethane. According to this technique, the agglomerating fluidized bedwas to operate adiabatically. Temperature control could be effected byadjusting the rate of supply of the coal and the temperature andpressure of the hydrogen-containing gas which fluidized the bed andoptionally by adding methane to the hydrogen to reduce the potentialextent to which the hydrogen may react with the coal to form methane inaccordance with the quasi-equilibrium which limits this reaction.

My aforementioned application Ser. No. 754,226 disclosed a technique forcarbonizing coal or cracking oil by supplying the coal or oil to thelower zone of a fluidized bed, this zone comprising coke pellets at atemperature. such that the coal or oil would carbonize or crack thereinto form gaseous fuel products and fresh coke which accretes upon thepellets. The gaseous products along with hydrogen would fluidize asuperposed, contiguous, upper zone of the fluidized bed, the upper zonecomprising a commingling of the coke pellets and a solid of smaller sizecontaining a substance avid for sulfur from hydrogen sulfide, such ascalcium oxide. The upper zone was fluidized at lower velocity than thelower zone, and the velocity of the lower zone was to be suflicient toprevent the smaller solid from penetrating deeply into the zone. Meanswere provided to effect a commingling of the coke pellets and thesmaller solid in the upper zone, and the fresh coke was desulfurizedthrough the cooperative action of the hydrogen and the sulfur-avidsolid. Fuel gas and coke, each low in sulfur, were withdrawn from thefluidized bed.

SUMMARY OF THE INVENTION The invention relates to an improved method forcarbonizing coal or cracking residual oil under conditions which areagglomerating with respect to the coke product.

An object of the invention is to provide an improved process forconverting caking coals or residual oils into a gaseous product andcoke.

Another object is to provide processes yielding a methane-rich gas orother fuel gas and coke starting from coal, including bituminous andsub-bituminous coals and lignites, many of which are not ordinarilyconsidered to be caking coals, or from fluid hydrocarbonaceous fuel suchas residual oil, bitumen, pitch, tar, kerogen, and the like.

Another object is to provide processes to produce a synthetic fuel gasof pipeline grade according to U.S. standards for such a gas.

Another object is to provide processes to produce liquid fuels from coalor lighter liquids from heavy residual oils.

More specifically, the invention relates to an improved method forsupplying heat to (or removing heat from) a fluidized-bed zone in whichcoal or oil undergoes carbonization or cracking (i.e., pyrolysis) underconditions which are agglomerating with respect to the coke product. Theimproved method provided by the instant invention greatly enlarges therange of applicability of the broad idea disclosed in my aforementionedapplication Ser. No. 561,551, to become US. Pat. 3,437,561, forcarbonizing coal in a manner such that the coke product is produced inform of agglomerated coke pellets. In my earlier disclosure, the bed wasoperated adiabatically. Ac cordingly, the range of suitable variablessuch as hydrogen pressure, temperature, and coal feed rate wasrelatively narrow. If the bed could be operated non-adiabatically, witheither supply or withdrawal of heat, the range of these variables couldbe appreciably broadened without departing from conditions which areotherwise operable. Providing heat-transfer surface within theagglomerating fluidized bed of the earlier disclosure is not anattractive idea, since the surface would be subjected both to foulingconditions on account of the stickiness of the reacting coal and also tolarge mechanical stresses on account of the rapid movement of largemasses of coke pellets which are fluidized at a relatively high.fluidizing-gas velocity, advantageously 5 or more feet per second(ft/sec.) on the superficial basis according to my earlier disclosure.

In examples described in the specification of my aforementionedapplication Ser. No. 754,226, heat was supplied to an agglomeratingfluidized-bed zone of the above-described type by direct conduction ofheat from a superposed, contiguous fluidized-bed zone. In other words,this disclosure indicated a way whereby the agglomerating bed could beoperated in a nonadiabatic manner.

According to the instant invention, there is provided method andapparatus for pyrolyzing a solid or liquid hydrocarbonaceous fuel. Thefuel is charged to a first zone of a fluidized bed, this zone comprisingpellets of coke at a temperature suflicient to cause pyrolysis of thefuel to occur with production of fuel gases and a coke product adheringto and accreting upon the pellets. Heat is imparted to a second zone ofthe fluidized bed, or heat is withdrawn therefrom, to maintain thetemperature of the fluidized bed substantially constant, this secondzone being superposed on the first zone and contiguous therewith andreceiving fluidizing gas therefrom. The second zone is fluidized atlower velocity than the first zone, and the solid of the second zonecomprises particles of sizes smaller than the coke pellets. The firstzone is fluidized at a velocity high enough that the smaller solid issubstantially prevented from sinking deep within this zone. Theaforementioned heat flows by conduction between the first and secondzones. Fuel gas is withdrawn from the second zone, and coke pellets arewithdrawn from the fluidized bed.

The term solid or liquid hydrocarbonaceous fuel as here used embraces,as a first category, solid fuels which when heated either exhibit asoftening temperature or begin to decompose with deformation and, as asecond category, fuels normally liquid at room temperature and solidfuels which when heated exhibit a melting temperature and can thereafterbe pumped.

Suitable fuels of the first category for practice of the invention areto be found among bituminous and subbituminous coals and lignites,including many coals ordinarily considered non-caking when viewed inlight of conventional atmospheric-pressure coal-carbonizationprocedures. To use some of the non-caking coals or lignitessuccessfully, one must operate the process of the invention at a highpressure and provide for presence of a high partial pressure of hydrogenin the first zone. It is to be understood that bituminous andsubbituminous coals and lignites may be altered by a partialcarbonization or a partial oxidation or a reduction in the intrinsicmoisture (as, for example, in the drying of lignites by the FleissnerProcess). Suitable fuels of the first category are also to be foundamong such altered coals and lignites, provided the altered materialdoes not contain more than 91 weight percent carbon on amoisture-and-ash-free basis and display a hydrogen-to-carbon atomicratio below 0.6.

Fuels of the second category include petroleum fractions from thegas-oil range and heavier, but the greater practical interest lies inapplication of the instant invention to treatment of fuels of the secondcategory which are generally characterized by high specific gravity, lowhydrogen content, a significant aromatic content, and a Conradson carbongreater than about 1 percent, usually greater than 2 percent. Examplesof the latter fuels are residual fuel oils, cracked residua, asphalts,asphalt fractions prepared from residua by solvent extraction, heavycoker tars, coal tars, pitches, bitumens, carbonaceous matter from tarsands, gilsonite, kerogens, carbonaceous matter from oil shales, and thelike.

A temperature greater than about 900 F. is generally sufficient to bringabout some carbonization of a solid fuel or cracking of a liquid fuelcharged to the bed of coke pellets. A temperature greater than about1,000 F. is preferred, and a temperature up to about 1,700 F. isgenerally serviceable. The fuel is heated almost instantaneously to thebed temperature, and converted almost instantaneously by rapid, initialcarbonization or cracking reactions into light gaseous products and aresidue of sticky matter which adheres to a pellet of coke. The stickymatter is converted to a thin patch or layer of fresh dry coke by later,slower carbonization or cracking reactions which give rise to evolutionof further gaseous or vapor products. In general, the sticky matter hasa life on the order of only a few seconds between its formation by theinitial reactions and its conversion into a dry coke.

When the combined heat effect of all of the carbonization or crackingreactions which occur in the first, agglomerating zone is endothermic,the process of the invention provides a way to supply heat to this zone,i.e., by conduction from the second zone. A variety of means may beemployed for imparting this heat to the second zone so that thetemperature of the fluidized bed may be kept substantially constant intime.

Solid may be supplied to the second zone at a higher temperature thanthe temperature of the fluidized bed, and solid may be withdrawn fromthe second zone to maintain a substantially constant inventory of solidtherein.

Heat may also be generated in the second zone by a variety of chemicalreactions, such as:

1) a chemical reaction between a constituent of the fluidizing gas andthe aforementioned hot solid supplied to the second zone; for example,the solid might contain CaO and the fluidizing gas might contain CO at apartial pressure greater than the equilibrium decomposition pressure ofCaCO at the temperature of the fluidized bed, or the gas might containCO and steam as well as CO the combined partial pressure of the CO andCO exceeding the aforementioned equilibrium decomposition pressure andthe CO and steam being converted to CO and H in the fluidized bed;

(2) a combustion reaction supported by the fuel gases entering thesecond zone from the first zone and by air or other gas containingoxygen injected into the second zone, the oxygen in the air or other gasbeing preferably supplied at a rate below the stoichiometric forcomplete combustion;

(3) a reaction between a hydrocarbon of aliphatic character orcontaining aliphatic groups and hydrogen arising from the carbonizationor present in the fluidizing gas to the first zone or arising fromconversion and CO and steam to CO and H in the fluidized bed, thereaction yielding methane.

Heat may also be supplied to the second zone by indirect heat exchangefrom a fluid heating medium, such as helium or liquid sodium.

If the hydrogen partial pressure in the fluidizing gas to the first,agglomerating zone is sufficiently great, the

combined heat effect of the hydrocarbonization or hydrocrackingreactions which occur therein can be exothermic. In this circumstance,the process of the invention provides a way to remove heat from thiszone, i.e., by conduction to the second zone. This heat may be withdrawnfrom the second zone by indirect heat exchange to a fluid coolingmedium, such as water. Heat may also be withdrawn from the second zoneby injecting a vaporizzable liquid therein.

Both the coke pellets and the smaller solid should be present in a rangeof particle sizes, preferably a range such that substantially thelargest particle in each solid is at least about five times larger thansubstantially the smallest particle in the solid. The largest particlein the smaller solid should preferably be less than one-half thediameter of the smallest of the coke pellets.

The preferred way to ensure that the second zone is fluidized at a lowervelocity than the first zone is to provide a second zone larger incross-sectional area than the first zone.

It is preferable to Withdraw coke pellets from the bottom of the first,agglomerating zone, but a suitable procedure is to withdraw both cokepellets and the smaller solid from the second zone. The mixture of thetwo solids can be readily separated on account of their difference insize, either byelutriation or by screening.

The fluidizing-gas velocity in the first zone should preferably be lessthan 10 times greater than the minimum fluidization velocity of the cokepellets. The ability to select velocity whereby the lower elevations ofthe first zone are maintained substantially free of the smaller solidmay be understood by considering the events which occur when a bed ofparticle is fluidized by a gas at ever higher velocities. As velocity isgradually increased, the density of the fluidized bed decreases, but therate of decrease in density with increase in velocity is not marked.Ultimately, however, a critical velocity is abruptly reached at whichthe density of the bed drops sharply; the bed appears suddenly to thinout. Unless the Vessel containing the bed is extremely tall, the gaswill convey most of the bed overhead and away from the vessel. Thiscritical velocity may be termed the dilute-phase transition velocity. Anattempt to fiuidize the particles at a higher velocity merely produces adilute phase having a voidage usually well over 90 percent. If a smallparticle is injected into a gas-fluidized bed of relatively far largerparticles, the smaller particle will tend to rise toward the top of thebed if its size and density are such that its dilute-phase transitionvelocity, in a bed comprising an aggregation of like smaller particles,is appreciably below the actual fluidizing velocity in the bed of largerparticles. The largest particle of the smaller solid employed in thesecond zone of the fluidized bed of the instant invention should be suchthat it would tend to rise toward the top of the fluidized bed of cokepellets comprising the first zone.

The smaller solid is preferably fluidized in the second zone at afiuidizing-gas velocity at least about 10 times greater than the minimumfluidization velocity of the solid. The dilute-phase transition velocityof the smaller solid is preferably not more than about 50 percent largerthan the minimum fluidization velocity of the coke pellets takenaltogether. The fluidization velocity in the second zone should be lessthan the dilute-phase transition velocity of the smaller solid.

A wide range of solid substances may be used for the smaller solid ofthe second zone, but in general materials of lower density will bepreferred over materials of higher density. The fluidized density of thesolid should be less than the true density of the coke pellets.

Coke pellets will tend to geyser from the lower zone upward into theupper zone. The smallest coke pellet should preferably have a minimumfluidization velocity, in a bed comprising an aggregation of likepellets, above the actual fiuidizing-gas velocity in the second zone, sothat a coke pellet ejected from the first zone into the second zone willtend to sink back downward into the first zone.

The circulation of coke pellets between the two zones provides theprincipal mechanism whereby heat is conducted from one zone to theother. In most applications of the invention, the temperatures of thetwo zones will differ from one another by at the most a few degrees. Ifthe temperatures differ too greatly, they may be brought closer togetherby providing means to increase the circulation of coke pellets from thelower zone into the upper zone. For example, a vertical pipe or risercould be provided extending from near the top of the lower zone wellinto the upper zone, transport gas being supplied to the bottom of thepipe to convey coke pellets upward therein.

Considering the ranges of fluidizing-gas compositions, temperatures, andpressures which may be encountered, and considering the range of densityof materials which are candidates for the smaller solid, I am not ableto give precise numerical values covering all circumstances to governthe particle sizes for the smaller solid and for the coke pellets and toprescribe the fluidizing velocities in the two zones. Suitable sizes andvelocities can be readily established by experiment. I believe that theexperimentation can be usefully guided by the foregoing remarksconcerning the critical size of particle which tends to rise or to sinkin a fluidized bed of larger or smaller particles respectively. Thefluidizing-gas velocity in the first zone is preferably greater thanabout ft./sec., and a suitable minimum size of coke pellet willgenerally be found to be on the order of inch or larger. Thefluidization velocity in the second zone is suitably between about 0.5and 5 ft./ sec. and preferably between about 0.8 and 4 ft./ sec. Asuitable maximum size of particle of the smaller solid will generally befound to be on the order of 40-mesh (U.S. Standard) or smaller.

Successful operation of the process of the invention depends criticallyupon commencing the operation with a suitable starter bed of solidpresent in the first zone. The starter bed should comprise a startersolid displaying a range of particle sizes, preferably at leastfive-fold, and with a smallest particle not substantially smaller thanthe minimum size desired for the coke pellets to be made. The starterbed need not be carbonaceous, a solid suitable for use at hightemperature and having a density between about and pounds per cubic footbeing generally satisfactory.

During operation of the process of the invention, seed particles shouldbe added to the first zone to provide new particles on which coke mayaccrete. The number of such seed particles added during a givenoperating interval should be substantially equal to the number of cokepellets withdrawn from the bed. The size of each seed particle shouldpreferably be approximately equal to the size of the smallest cokepellet. Seed particles may be conveniently provided by suitably crushingand screening a portion of the coke pellets withdrawn from. the bed.

Coal or other solid fuel for treatment by the process of the inventionis advantageously ground to a fineness substantially smaller thanIOU-mesh before it is charged to the first zone.

The coke pellets produced by the process of the invention are anexcellent fuel for fluidized combustion either by the technique whereinheat is removed from the combustion to boiler tubes in contact with thefluidized bed or by the technique of Godel [U.S. Pat. 2,866,696 (1958)].The coke pellets are also a good material for gasification in aslagging-grate gasifier [U.S. Pat. 3,253,906 (1966)], or for briquettingand calcining to produce a coke for metallurgy or for electrodes.

DESCRIPTION OF THE DRAWINGS The invention including various novelfeatures will be more fully understood by reference to the accompanyingdrawings and the following description of the operation of thealternatives illustrated therein:

FIG. 1 is a schematic diagram illustrating a process and apparatus forcarbonization of coal in a manner such that the fuel gas and cokeproducts are substantially free of sulfur. The agglomerating zone isendothermic, and heat is imparted to the second zone both by supplying ahot solid to this zone and by reaction of CaO with CO to form CaCOtherein.

FIG. 2 is a schematic diagram illustrating an embodiment of theinvention in which fluid matter may be in jected into the second zone.The fluid matter might be air or a gas containing oxygen to producecombustion reac tions in the second zone, or a light naphtha to reactwith hydrogen exothermically in the second zone to produce methane, or avaporizable liquid to vaporize and withdraw heat from the second zone.

FIG. 3 is a schematic diagram illustrating an embodiment in whichheat-exchange surface, either for supply or withdrawal of heat, isplaced in the second zone.

FIG. 4 is a schematic diagram illustrating an embodiment directed towardproduction of a fuel gas rich in methane and hydrogen as well as coke,the fuel gas being suitable for further processing to produce a gas ofpipeline grade according to U.S. standards for such a gas.

The embodiments of FIGS. 3 and 4 are suitable for production of liquidas well as gaseous fuels from coal.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Carbon 80.70 Hydrogen 5.47Sulfur 3.72

Nitrogen 1.62

Oxygen 8.49

Grinding equipment 2 reduces the coal to a particle size such thatsubstantially all of the coal passes through a IOO-mesh screen (U.S.Standard). Coal is supplied from equipment 2 via conduit 3 to heatingequipment 4, where the coal is dried and its temperature is raised to300 F. The coal is transferred from equipment 4 via line 5 to locksystem 6. The coal in line 5 carries 28,456 pounds per hour of intrinsicmoisture, and is accompanied by steam at 300 F. and 25 pounds per squareinch absolute (p.s.i.a.).

Gas is supplied to the process at 397 p.s.i.a. and 700 F. via line 7.The rates of supply of the several constituents in the gas are asfollows, expressed in pound-moles per hour (m./hr.):

A fraction 0.31684 of the gas is supplied via line 8 to lock system 6,where the gas is used to raise the pressure of the coal to 397 p.s.i.a.,and the gas and coal are injected together at a substantially constantrate into coal-carbonization vessel 9 via a multiplicity of lines 10 andnozzles 11. For simplicity of the drawing, only one line 10 and onenozzle 11 are shown. The remaining gas from line 7 is supplied via line12 to gas-heating equipment 13 and thence at 1300 F. to the bottom ofvessel 9, to provide (together with gas from lines 10 and nozzles 11)the fluidizing gas for fluidized bed 14 housed in a lower part of vessel9.

Coal-carbonization vessel 9 houses two regions in which particulatesolids are maintained in the fluidized state: fluidized-bed 14 at 1400F. occupies a lower part of vessel 9, and fluidized region 15 at 1740 F.occupies an upper part of vessel 9. Particulate solids are maintained inthe dense-phase fluidized condition in bed 14, and they are maintainedin the dilute-phase fluidized condition in region 15. The pressure atthe bottom of bed 14 is 350 p.s.1.a.

Bed 14 comprises two superposed, contiguous fluidizedbed zones: a lowerzone 16 comprising pellets of coke of a size suitably ranging from aboutinch in diameter to about /4 inch, and an upper zone 17 comprising asolid derived from naturally-occurring dolomite rock of a particle sizesuitably ranging from about 40-mesh to about 325-mesh. OlTgases fromzone 17 convey the dolomitederived solid across void space 18 and intoregion 15.

Zone 16 is an agglomerating coal-carbonization zone, which preferablyhas the form of a frusto-conical chamher with a gradual taper and thesmaller end at the bottom. The fluidizing-gas velocity is suitably 20ft./sec. at the bottom of zone 16, and is suitably 15 ft./sec. at thetop. Coal entering zone 16 is heated almost instantaneously tosubstantially the bed temperature, and carbonization of the coal isinitiated practically instantaneously. Almost at once, the coal is splitinto a gaseous fraction, comprising mainly methane and hydrogen, and asticky, semi-fluid residue. The latter is captured by a coke pellet,sticking thereto to form a smear upon the surface of the pellet. Zone 16of coke pellets serves as a dust trap for the sticky initialcarbonization residue. Further coking reactions, which occur moreslowly, transform the sticky smear into dry coke and cause additionalgases and vapors to be evolved. However, the residue of carbonizationremains sticky for only a time on the order of a very few seconds.

Coke product is withdrawn from zone 16, to maintain the inventory ofcoke pellets therein substantially constant, via pipe 19 at the bottom.The m.a.f. coke has the following analysis (expressed in weightpercent):

8 Carbon 95.92 Hydrogen 1.33 Sulfur 0 .30 Nitrogen 1.43 Oxygen 1.02

The rate of coke production is 333,057 pounds per hour on an m.a.f.basis.

The diameter of zone 17 is appreciably greater than the diameter of zone16, and the fluidizing-gas velocity in zone 17 is suitably 2 ft./ sec.Heat is generated or developed in zone 17 by mechanisms to be elucidatedhereinafter, the heat being communicated or conducted from zone 17 tozone 16 by virtue of the contiguity of these fluidized-bed zones. Cokepellets geyser upward from zone 16 into the middle of zone 17, minglingtherein with the dolomitederived solid. The fluidizing-gas velocity inzone 17 is too small for a large inventory of coke pellets to bemaintained permanently in this zone, and the coke pellets which enterzone 17 gravitate downward and back into zone 16. The fluidizing-gasvelocity in zone 16 is too large for particles of the dolomite-derivedsolid to sink deep within this zone. The bottom of zone 16, where manyof the coke pellets are partially covered with sticky matter arisingfrom the initial carbonization reactions, is substantiallv free ofparticles of the dolomite-derived solid.

The dolomite-derived solid of zone 17 comprises an intimateintermingling of microscopic crystallites of CaCO CaO, Gas, and MgO.Natural dolomite, the double carbonate of calcium and magnesium, seldomcontains these tWo elements in precisely one-to-one atomic ratio, thecalcium usually being present in excess. Ideally, however, dolomite maybe written CaCO -MgCO Solids derived by half-calcining orfully-calcining dolomite may be written [CaCO -l-MgO] and [Ca0+MgO]respectively, to signify the fact that neither of these solids is a truechemical species, but comprises an intimate intermingling ofcrystallites of the chemical species included between the brackets. Thesolid derived by allowing one of these solids to absorb sulfur may bewritten [CaS+MgO]. The dolomite-derived solid in zone 17 suitablycomprises 2 parts CaCO 1 part CaO, 1 part C218, and 4 parts MgO, on amolar basis.

Sulfur in form of H 5 arises in vessel 9 not only as a direct result ofcarbonization of the coat but also as an indirect result of cracking oftar species and of attack by hydrogen upon coke. Substantially all ofthe H 8 reacts with the dolomite-derived solid in zone 17, thus:

[CaO-l-MgO] +H S= [CaS+MgO]-]H O (1) The dolomite-derived solid alsoabsorbs CO in zone 17:

[Ca0+MgO] +CO [CaCO |-MgO] (2) The crystallites of MgO in thedolomite-derived solid are catalytic for the water-gas-shift reaction,

H 0+CO=H +CO (3) The solid is extremely effective in promoting theconversion of CO to H by the summation of reactions (2) and (3):

[CaO-l-MgO] +H O+CO= [CaCO +MgO] +H (4) Region 15 is a calcination zone.The flow of materials across space 18, from bed 14 to region 15,comprises (expressed in m./hr.)

C H 391.9 as; a CaO 1,659.2 MgO 6,636.8

CO 6,259.3 H 9,078.1 CO 3,221.1 H O 6,799.5 H S 18.2 COS 0.6 N 19,8117 A247.1

The gases flowing from the several cyclones 23 are brought together inline 24 and delivered from the process. Fluidizing gas in line 7represents a return to the process of of this gas.

Solid separated from the gas in each line 22 is delivered from eachcyclone 23 to a standpipe 25 fitted with a solidflow-regulating valve26. The flows of solid through the several valves 26 are suitablyregulated so that a return of solid via pipes 25 and valves 26 to thebottom of region 15 produces a loading of solid in the gas rising upwardthrough region 15 and also in each line 22 on the order of one pound ormore of solid per actual cubic foot of gas. The effect of cyclones 23,standpipes 25, and valves 26 is to recircualte a large flow of solidfrom the top to the bottom of region 15. This recirculation of solidserves to maintain the temperature throughout region 15 substantiallyuniform and thereby to reduce the likelihood of the occurrence of smallzones wherein the temperature might rise to a level such that thedolomitederived solid would sinter and lose its chemical reactivitytoward H 8 and CO One of the standpipes 25 is fitted with abranch-standpipe 27, which delivers solid via solid-flow-regulatingvalve 28 to zone 17 of fluidized-bed 14. The solid passing throughbranch standpipe 27 and valve 28 comprises (expressed in m./hr.):

The flow of solid through valve 28 may advantageously be used as aprimary control on the temperature of bed 14, although the temperatureof fiuidizing-gas in line 12 and the rate of flow of coal in line 10 mayalso be used as control variables if desired.

In order to permit the rate of flow of solid through valve 28 to be usedas a primary control of the temperature of bed 14, it is advantageousthat at least one of the standpipes 25 have a diameter suflicient toprovide room for a significant inventory of the dolomite-derived solidin the dense-phase condition. Changes in the flow through valve 28 canbe reflected by changes in this inventory, so that frequent withdrawalsof this solid from vessel 9 or additions thereto may be avoided.

In order to maintain the reactivity of the dolomitederived solid at ahigh level or to replace losses of solid which pass from cyclones 23into line 24, it is advantageous to add relatively small quantities ofdolomite intermittently from the line 40 to line 27 via valve 41. Line40 may also be used to add seed particles of coke, suitably of about thesame size as substantially the smallest coke pellet in zone 16, at aparticle-number rate sub- 10 stantially equal to the particle-numberrate of withdrawal of coke product from zone 16 via pipe 19. Inaddition, line 40 may be used to add a bed of a starter solid to zone 16prior to starting to operate the process of FIG. 1. A preferred startersolid comprises coke pellets of the aforementioned size range.

Each of the aforementioned reactions (1), (2), (3), and (4) areexothermic. Heat is generated in zone 17 by these reactions, and heat isalso developed in zone 17 by the cooling of the solid entering the zonefrom line 27. This solid is cooled from 1740 F. to 1400 F. in zone 17.Heat is conducted from zone 17 to zone 16 by virtue of the directcontact of these contiguous fluidized-bed zones, the heat serving tofurnish the endothermic heat needed for the coal-carbonization processoccurring in zone 16.

Solid in the following amount (expresed in m./hr.) is withdrawn fromzone 17 via line 29:

CaCO 1,550.0 CaS 775.0

CaO 775.0 MgO 3,100.0

This solid is delivered to sulfur-recovery system 30, wherein sulfur maybe extracted from the solid according to the teachings of my US. Pat.3,402,998 (Sept. 24, 1968). System 30 returns a solid at 1200 F. to zone17 via line 31, the solid comprising (expressed in m./hr.)

CaCO 2,846.6 CaS 253.4 MgO 3,100.0

If a low-sulfur coal is to be treated, or. if a high-sulfur coal is tobe treated but a low-sulfur coke is not required, the operation of theequipment depicted schematically in FIG. 1 can advantageously bemodified as follows: Alter the temperature and/or the pressure in region15 so that CaCO will not decompose therein according to the reverse ofreaction (2). This might be done by lowering the temperature and/or byraising the pressure, so that the partial pressure of CO in region 15 isgreater than the equilibrium decomposition pressure of CaCO In general,a higher rate of circulation of solid from region 15 viabranch-standpipe 27 and valve 28 will be required in order that thecooling of this solid in zone 17 will provide the endothermic heat.necessary for zone 16. In general, according to this modification of theoperation of equipment shown in FIG. 1, the sulfur content of the fuelgas in line 23 will be higher than that indicated previously, but maystill be sufiiciently low for many purposes which this gas might serve.

Residual fuel oil or other solid or liquid hydrocarbonaceous fuel oftypes hereinbefore described could be substituted for the coal suppliedto vessel 9 via lines 10 and nozzles 11.

If recovery of sulfur is not required, the dolomitederived solid couldbe replaced by sand or preferably a less dense solid derived from a clayor other solid suitably inert chemically with respect to the gasespresent in fluidized-bed \14 and fluidized region 15. However, for thissituation, a simpler apparatus is provided by the equipment depictedschematically in FIG. 2. In the figure, vessel 109 serves essentiallythe function of the lower part of vessel 9 in FIG. 1. Equipment items110, 112, 114, 116, 117, and 119 operate substantially in the manneralready described in connection with items 10, 12, 14, 16, 17, and 19respectively of FIG. 1 (with the exception of the method whereby heat isdeveloped in zone 1117). Heat is generated in zone 117, to betransmitted to zone 116, by the partial combustion of fuel through theagency of air or other gas containing oxygen introduced into zone 117via a multiplicity of lines 120 and nozzles 121. A fuel gas produced inzone 117 is separated from dust by cyclone gas-solid separator 123, andthe gas is delivered via line 124. The solid fluidized in zone 117 issuitably a sand or 11 an alumina or an alumina-silicate or even finesizes of coke. Make-up solid for zone 117 and seed particles for zone116 may be added from line 140 via valve 14-1. Prior to start-up to theequipment, line 140 may be used to supply a bed of a suitable startersolid to zone 116.

If a fuel gas undiluted by nitrogen is required, substantially pureoxygen may be supplied to zone 117 via lines 120, and recycle gas fromline 124 may be employed as fluidizing gas supplied from line 112.

If a fuel gas undiluted by nitrogen and rich in methane is required, apossibility would be to employ a fluidizing gas rich in hydrogen and lowin nitrogen in line 112 of FIG. 2 and to supply a material to zone 117via lines 120 capable of reacting exothermically with hydrogen toproduce methane. If this possibility is elected, the pressure should beappreciably above atmospheric, suitably atmospheres or greater. Asuitable material to react with hydrogen would be ethane or propane orother aliphatic hydrocarbon containing 2 or more carbon atoms. A lightnaphtha would be a suitable material, as would also aromatic materialscontaining aliphatic side-chains, such as toluene or xylene or ethylbenzene or the like.

Alternatively, if a fuel gas undiluted by nitrogen is required, theembodiments depicted in FIGS. 3 and 4 may be preferred. Equipment items109, 110, 112, 114, 116, 117, 119, 123, 124, 140 and 141 in each ofFIGS. 3 and 4 operate substantially in the manner already described inconnection with these items in FIG. 2 (with the exception of the methodwhereby heat is developed in zone 117 The fluidizing gas in line 112 ispreferably low in nitrogen, and may advantageously comprise at least inpart a recycle of a portion of the fuel gas product in line 124.

In FIG. 3, zone 117 houses heat-exchange surface 132, whereby heat istransferred by indirect heat exchange from a hot fluid medium to zone117, to flow by conduction therefrom to zone 116. Suitable hot fluidmediums are liquid sodium metal and helium gas, for example.

In FIG. 4, vessel 209 serves essentially the function of the upper partof vessel 9 in FIG. 1; and equipment items 215, 222, 223, 224, 225, 226227, and 228 operate substantially in the manner already described inconnection with items 15, 22, 23, 24, 25, 26, 27, and 28 respectively inFIG. 1 (with the exceptions of the methods whereby air, fuel, and solidare introduced into region 215). Air or other gas containing oxygen issupplied as fluidizing gas to the bottom of vessel 209 from line 220.Fuel is supplied to region 215 from a multiplicity of lines 233 andnozzles 234 (for simplicity, only one line 223 and one nozzle 234 areshown in FIG. 4). Solid is transferred from zone 117 of vessel 109 toregion 215 of vessel 209 via line 235 and solid-flow-regulating valve236; the rate of the transfer is regulated to maintain a substantiallyconstant inventory of solid in zone 117. The fuel supplied to region 215may sometimes advantageously comprise the same fuel as that supplied vialine 110 to zone 116 of vessel 109, especially if this is a fluid fuel.Alternatively, the fuel to region 215 may sometimes advantageouslycomprise either a portion or all of one of the two fuel products fromvessel 109, the coke in line 1.19 or the fuel in line 124. Anotheralternate arises if the fuel gas in line 124 contains significantquantities of condensibles, such as benzene, toluene, etc. In thiscircumstance, the fuel to region 215 may sometimes advantageouslycomprise either the gaseous fraction or the liquid fraction arising fromthe fuel gas in line 123 after it has been cooled.

The embodiment of FIG. 4 may be used to produce a gas rich in methaneand hydrogen in line 124 from either a coal or a residual oil feed inline 110. This may be accomplished with a supply of a dolomite-derivedsolid from line 227 to zone 117, the solid containing either CaO or CaCOalong with CaS and MgO. If this is done, a system for sulfur recoverymay advantageously be added to FIG. 4, like system 30 of FIG. 1.Alternatively, the solid supplied to zone 117 from line 227 may suitablybe a sand or an alumina or an alumina-silicate or a fine coke.

The aforementioned gas rich in methane and hydrogen would be suitablefor further processing to yield a synthetic pipeline gas having aheating value on the order of 920 or more British thermal units perstandard cubic foot. This further processing might advantageouslyinclude an operation in which condensibles in the gas in line 124 aresubjected to a hydrodealkylation treatment, which may sometimesadvantageously employ hydrogen present in the non-condensible fractionof the gas from line 124.

The embodiments described above in connections with FIGS. 3 and 4 aresuitable for modification in direction of greater yield of condensiblefuel products and lesser yield of methane or other light hydrocarbons.Such a modification may be brought about by lowering the temperature ofbed 114. For maximum production of liquid products, this temperatureshould be between about 900 and 1100 F.

If a hydrocarbonaceous fuel, such as bituminous coal or residual oil, istreated in the apparatus of FIG. 3 by a gas from line 112 containinghydrogen at a sufliciently high partial pressure, the hydrocarbonizationor hydrocracking reactions occurring in zone 116 will be exothermic,rather than endothermic as in the embodiments previously described. Thisheat may be removed from vessel 109 by providing a cooling medium toheat-exchange surface 132. A suitable cooling medium is water, forexample, and the heat transferred from zone 117 to the water mayadvantageously be employed to generate high-pressure steam.Alternatively, the apparatus of FIG. 2 might be used, and a vaporizableliquid such as water could be added directly to zone 117 via lines 120and nozzles 121, the latent heat of the water flashing in zone 117taking up the exothermic heat passing by conduction from Zone 116 intozone 117.

I do not wish my invention to be limited to the particular embodimentsillustrated in the drawings and described above in detail. Otherarrangements will be recognized by those skilled in the art, as well asother purposes which the invention can serve.

I claim:

1. A process for pyrolyzing a solid or liquid hydrocarbonaceous fuel,comprising:

(a) providing a fluidized bed comprising first and second zones, saidfirst zone comprising pellets of coke, said second zone being superposedon said first zone and contiguous therewith and receiving fluidizing gastherefrom and comprising a particulate solid having particles of sizessmaller than said coke pellets, said first zone being fluidized at asuperficial gas velocity sufliciently great as to substantially preventthe substantially largest particle of said solid from sinking deeptoward the bottom of said first zone, and said second zone beingfluidized at a superficial gas velocity sufficiently small as to allowthe substantially smallest pellet of said pellets of coke to sinkdownward within said second zone and to reenter said first zone,

(b) charging a solid or liquid hydrocarbonaceous fuel to said firstzone,

(c) causing heat to flow by conduction between said first and secondzones in an amount and direction to maintain a substantially constanttemperature in said first zone, said temperature being sufficient tocause pyrolysis of said fuel to occur with production of fuel gases anda coke product adhering to said pellets,

(d) withdrawing fuel gas from said second zone, and

(e) withdrawing coke pellets from said fluidized bed.

2. The process of claim 1 in which said direction of flow of said heatin step (c) is from said second zone to said first zone, and in whichheat is imparted to said second zone.

3. The process of claim 1 in which said direction of flow of said heatin step (c) is from said first zone to said second zone, and in whichheat is Withdrawn from said second zone.

4. The process of claim 1 including the step of providing seed particlesof coke to said first zone having a particle size substantially equal tosaid smallest pellet, the particle-number rate at which said seedparticles are provided being substantially equal to the particle-numberrate at which said coke pellets are withdrawn from said fluidized bed instep (e).

5. A process for pyrolyzing a solid or liquid hydrocarbonaceous fuel,comprising:

(a) charging a solid or liquid hydrocarbonaceous fuel to a first zone ofa fluidized bed, said first zone comprising pellets of coke at atemperature sufficient to cause pyrolysis of said fuel to occur withproduction of fuel gases and a coke product adhering to said pellets,

(b) imparting heat to a second zone of said fluidized bed to maintainsaid temperature substantially constant, said second zone beingsuperposed on said first zone and contiguous therewith and receivingfluidizing gas therefrom and comprising a particulate solid havingparticles of sizes smaller than said coke pellets, said first zone beingfluidized at a superficial gas velocity sufliciently great as tosubstantially prevent the substantially largest particle of said solidfrom sinking deep toward the bottom of said first zone, said second zonebeing fluidized at a superficial gas velocity sufficiently small as toallow the substantially smallest pellet of said pellets of coke to sinkdownward within said second zone and to reenter said first zone, saidheat flowing by conduction from said second zone to said first zone,

(c) withdrawing fuel gas from said second zone, and

(d) withdrawing coke pellets from said fluidized bed.

6, The process of claim 5 including the following steps: feeding aparticulate solid having particles of substantially said sizes to saidsecond zone at a temperature greater than said temperature, andwithdrawing solid from said second zone at a rate to maintain the solidinventory of said second zone substantially constant.

7. The process of claim 6 in which said particulate solid includescalcium oxide and the fluidizing gas to said second zone contains carbondioxide at a partial pressure exceeding the equilibrium decompositionpressure of calcium carbonate at said temperature.

8. The process of claim 6 in which said solid includes calcium oxide andthe fluidizing gas to said second zone contains carbon monoxide, steam,and carbon dioxide, the combined partial pressure of the carbon dioxideand carbon monoxide exceeding the equilibrium decomposition pressure ofcalcium carbonate at said temperature.

9. The process of claim 5 including the step of adding air or other gascontaining oxygen to said second zone to effect partial combustiontherein of said fuel gases, thereby generating heat in said second zone.

19. The process of claim 5 in which said second zone housesheat-exchange surface whereby heat is added to said second zone byindirect heat transfer from a fluid heating medium.

1'1. A process for pyrolyzing a solid or liquid hydrocarbonaceous fuel,comprising:

(a) charging a solid or liquid hydrocarbonaceous fuel to a first zone ofa fluidized bed, said first zone comprising pellets of coke at atemperature sufiicient to cause pyrolysis of said fuel to occur withproduction of fuel gases and a coke product adhering to said pellets,

(b) fluidizing said first zone with a gas containing hydrogen,

(0) withdrawing heat from a second zone of said fluidized bed tomaintain said temperature substantially constant, said second zone beingsuperposed on said first zone and contiguous therewith and receivingfluidizing gas therefrom and comprising a particulate solid havingparticles of sizes smaller than said coke pellets, said first zone beingfluidized at a superficial gas velocity sufiiciently great as tosubstantially prevent the substantially largest particle of said solidfrom sinking deep toward the bottom of said first zone, said second zonebeing fluidized at a superficial gas velocity sufliciently small as toallow the substantially smallest pellet of said pellets of coke to sinkdownward within said second zone and to reenter said first zone, saidheat flowing by conduction from said first zone to said second zone,

(d) withdrawing fuel gas rich in methane from said second zone, and

(e) withdrawing coke pellets from said fluidized bed.

12. The process of claim 11 in which said second zone housesheat-exchange surface whereby heat is removed from said second zone byindirect heat transfer to a fluid cooling medium.

References Cited UNITED STATES PATENTS 2,595,366 5/1952 ODell et a120136X 2,725,349 11/1955 Cahn et al 201--20X 2,970,893 2/1961 Viles23-181 3,194,644 7/1965 Gorin et 'al. 48-197 3,320,152 5/1967 Nathan etal. 201-12X 3,431,197 3/1969 Jahnig et a1. 2013 1X 3,443,908 5/1969Chaney et a1 20112X NORMAN YUDKOFF, Primary Examiner D. EDWARDS,Assistant Examiner US. Cl. X.R.

